1. Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display of active matrix type or the like which is driven by a thin film transistor (hereinafter, referred to as “TFT”) formed on a glass substrate, and a liquid crystal display manufactured by the method.
2. Description of the Background Art
In a process of manufacturing a liquid crystal display, especially in a process of manufacturing an active matrix type TFT liquid crystal panel, the process step in which something is in contact with a TFT array surface of a glass substrate is a brush cleaning step or a rubbing step before the panel assembly. A transparent conductive film which is to be display pixels is formed on a substrate surface in the brush cleaning and an orientation film is formed on a transparent electrode of the substrate surface in rubbing, and foreign matters such as transparent conductive film scraps, orientation film scraps, metal film scraps or the like are caused by contact between a cleaning roll brush or a rubbing roller cloth and the substrate surface. When such foreign matters are mixed into a display area, these make a short circuit between electrodes and irregularity in orientation of a liquid crystal, to cause a defect.
Among countermeasures against the above problem, i.e., prevention measures for scattering of various foreign matters into the display area in rubbing are a technique disclosed in e.g., Japanese Patent Application Laid Open Gazette No. 9-43629 (Patent Document 1: p. 8, FIG.4) where dummy pixels are formed around the display pixels, to acquire orientation film scraps and metal film scraps of the rubbing roller cloth by utilizing a level difference between the dummy pixels and a periphery of the dummy pixels, a technique disclosed in e.g., Japanese Patent Application Laid Open Gazette No. 2004-240142 (Patent Document 2: p. 11, FIG.2) where part of an orientation film is formed higher and by utilizing the level difference, the orientation film scraps and the metal film scraps of the rubbing roller cloth are acquired, and a case disclosed in e.g., Japanese Patent Application Laid Open Gazette No. 2001-318380 (Patent Document 3: p. 5, FIG.2) where projections and depressions are formed of an insulating film in a region where no orientation film is formed and foreign matters, the metal film scraps and the orientation film scraps attached to the rubbing roller cloth are acquired by the grooves.
In the conventional case where the dummy pixels are formed around the display pixels, the height of the dummy pixels from the glass substrate is equal to the height of the transparent conductive film and therefore transparent conductive film scraps caused in the brush cleaning step for cleaning a surface of a substrate before formation of the orientation film can not be sufficiently removed, and since the transparent conductive film is also formed on the dummy pixels, this technique produces an adverse effect for transparent conductive film scraps created from the dummy pixels in brush cleaning or rubbing.
Also in the conventional case where the level difference is formed by using the orientation film, no consideration is given to removal of the transparent conductive film scraps caused in the brush cleaning step for the substrate, which is performed before formation of the orientation film. Further, if an orientation film which is thicker than the thickness of the orientation film on the display area is formed in the peripheral region, there is a possibility that the orientation film is removed or chipped in rubbing, to cause orientation film scraps.
Still also in the case where an uneven portion for removing the foreign matters is formed outside the orientation film to acquire the fiber scraps of the rubbing roller cloth and the foreign matters and the orientation film scraps attached to the cloth, the transparent conductive film scraps can not be fully removed since the scraps are created also in a portion to which the orientation film is applied. Different from the fiber scraps of the rubbing roller cloth and the orientation film scraps, the transparent conductive film scraps are hard to remove even when cleaning with water or an organic solvent or supersonic cleaning is performed. Further, if the uneven portion for removing the foreign matters which is formed of a chromium film and an insulating film is manufactured by a presently general technique, the level of the portion becomes lower than the average level of the display area and therefore no sufficient effect of acquiring the foreign matters can not be produced in the brush cleaning step. Furthermore, in order to form the uneven portion for removing the foreign matters, an additional step of forming projections and depressions is needed, which leads to an increase in manufacturing cost.